CELLS AND EPITHELIAL MEMBRANES. 13 



pale, and finally disintegrates entirely ; its elementary 

 molecules, or granules, alone seem to possess the pro- 

 perty of resisting the action of this chemical agent. 



Although varying greatly in shape, all cells may be Different 

 arranged under one of the following distinctive types : 

 1st, spherical cells ; 2d, many-sided cells ; 3d, scales ; 

 4th, conical or cylindrical cells ; 5th, ciliated cells ; 

 6th, fusiform cells ; 7th, branching, or star-shaped 

 cells. 



To the first class belong the embryonic ovule, and Giobuiaror 



w spherical cells. 



the cells developed directly from it ; newly formed 

 cells in the adult, and, in general, all cells which float 

 in a liquid medium. 



The second class includes the deeper seated cells of Polygonal or 



many-sided cells 



many of the epithelial membranes ; the epithelial and 8cale8 - 

 cells of glands composed of clustered follicles, and of 

 some glands of tubular structure. Cells in the form 

 of scales are found only in the superficial layer of the 

 epidermis and epithelium of the tongue. 



The deep layer of almost all the epithelial mem- comcai ceiis. 

 branes which present a stratified arrangement of their 

 cells, the epithelium of the intestinal canal, and of its 

 tubular follicles, and that of a large proportion of the 

 excretory ducts of glands, are made up of conical or 

 cylindrical cells, (PL XXIII. fig. II. 3, PL XXVI. fig. 

 VI. fig. XL) 



The free surfaces of the epithelial cells lining the cmated ceiis. 

 walls of the air passages, uterus, fallopian tubes, etc., 

 are furnished with a great number of minute hair-like 

 projections (called cilia from their resemblance in 

 shape to an eye-lash) .which possess during life a 

 peculiar vibratile motion, always in the same direc- 



